There is an extensive description in the patent and other technical literature of photoelectrophoretic migration imaging processes.
Typically, photoelectrophoretic migration imaging processes employ a layer of electrostatic charge-bearing photoconductive particles, i.e., electrically photosensitive particles, positioned between two spaced electrodes, one of which may be transparent. To achieve image formation the electrically photosensitive particles positioned between the two spaced electrodes are subjected to the influence of an electric field and exposed to an image pattern of activating radiation. The charge-bearing electrically photosensitive particles migrate electrophoretically to the surface of one or the other of the spaced electrodes. As a result an image pattern is formed on the electrode surfaces. Typically, a negative image is formed on one electrode, and a positive image is formed on the opposite electrode.
Image discrimination occurs in the photoelectrophoretic migration imaging processes as a result of a net change in charge polarity of either the exposed electrically photosensitive particles (in the case of conventional electrophoretic migration imaging) or the unexposed electrically photosensitive particles (in the case of the electrophoretic migration imaging process described in U.S. Pat. No. 3,976,485 to Groner). Hence the image formed on one electrode surface is composed ideally of electrically photosensitive particles of one charge polarity, either negative or positive polarity, and the image formed on the opposite polarity electrode surface is composed ideally of electrically photosensitive particles having the opposite charge polarity, either positive or negative.
An essential component of any photoelectrophoretic migration imaging process is the electrically photosensitive particles. Ideally such particles should possess useful levels of electrical photosensitivity and good colorant properties.
Some particles which exhibit good colorant properties do not possess useful levels of electrical photosensitivity. Means for increasing the level of electrical photosensitivity of such particles are therefore desirable. Sensitizers for electrically photosensitive particles have been described in patents. For example British Patent Specification No. 1,193,276 states that in general such particles may be sensitized by the addition of Lewis acids or Lewis bases. This statement is not very useful however. Relative to any selected electrophotosensitive particle, there are many Lewis acids and many Lewis bases which will not sensitize the selected particle. Moreover, this kind of statement does not take into account the many variables affecting sensitization resulting from the electrophoretic migration imaging dispersion in which a potential sensitizer is included.
The phrase "electrically photosensitive pigment" as used herein refers to any pigment which, when placed between two electrodes, subjected to an applied electric field and exposed to radiation which said pigment absorbs, will migrate to one of the two electrodes.